In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Until recently, ultraviolet radiation such as g-lines and i-lines have been used as the exposure light source, but recently, KrF excimer lasers (248 nm) have been introduced, and even ArF excimer lasers (193 nm) are now starting to be used.
One example of a resist material that satisfies the high resolution conditions required to enable reproduction of a pattern of minute dimensions is a chemically amplified resist composition, which includes a base resin that displays changed alkali solubility under the action of acid, and an acid generator that generates acid on exposure, dissolved in an organic solvent (for example, see patent reference 1).
In KrF excimer laser lithography, polyhydroxystyrenes or derivatives thereof in which the hydroxyl groups have been protected with acid dissociable, dissolution inhibiting groups, which exhibit a high level of transparency relative to a KrF excimer laser (248 nm), have typically been used as the base resin of chemically amplified resists. However, these resins exhibit unsatisfactory transparency near 193 nm.
As a result, ArF resists with a variety of different compositions are now being proposed, and in these resists, the most common ArF resist base resins are (meth)acrylic resins, which exhibit a high level of transparency in the region of 193 nm.
In recent years, the rate of miniaturization has accelerated, and nowadays, resolutions capable of forming line and space patterns of no more than 100 nm and isolated patterns of no more than 70 nm are being sought. As a result, in addition to the research and development being conducted on resist materials to enable ultra-miniaturization, research is also being conducted on pattern formation methods, to develop techniques capable of overcoming the resolution limits of resist materials.
An example of one such miniaturization technique that has been recently proposed is the thermal flow process, wherein a resist pattern is formed using normal lithography techniques, and the resist pattern is then subjected to heat treatment to reduce the pattern size. Thermal flow is a method in which following formation of a resist pattern using photolithography techniques, the resist pattern is heated and softened, causing the pattern to flow towards the gaps in the pattern, thus reducing the resist pattern size, that is, the size of the portions where the resist is not formed (such as the hole diameter in a hole pattern, or the space width in a line and space (L&S) pattern).
For example, the patent reference 2 discloses a method for forming a fine pattern in which a resist pattern is formed on a substrate, heat treatment is conducted, and the cross-sectional shape of the resist pattern is changed from a rectangular shape to a semicircular shape, thereby increasing the length of the pattern base and forming a finer pattern.
Furthermore, the patent reference 3 discloses a method for forming a fine pattern in which following formation of a resist pattern, heating is conducted to approximately the softening temperature of the resist, and fluidization of the resist causes a narrowing of the pattern size.
Furthermore, the patent references 4 and 5 disclose methods that differ from the aforementioned thermal flow processes, wherein heating is used to shrink a water-soluble resin, thereby forming a finer pattern.
Patent Reference 1:
Japanese Unexamined Patent Application, First Publication No. 2002-162745
Patent Reference 2:
Japanese Unexamined Patent Application, First Publication No. Hei 1-307228
Patent Reference 3:
Japanese Unexamined Patent Application, First Publication No. Hei 4-364021
Patent Reference 4:
Japanese Unexamined Patent Application, First Publication No. 2003-107752
Patent Reference 5:
Japanese Unexamined Patent Application, First Publication No. 2003-142381
However, in this type of thermal flow process, because the resist is caused to flow by heating conducted after the developing step, a problem arises in that the cross-sectional shape of the side walls of the resist pattern are prone to collapse, causing a deterioration in the verticalness (rectangularity) of the pattern.
Because a shrink process does not cause the resist to flow, a resist pattern can be produced that exhibits more favorable rectangularity than that from a thermal flow process. However, until now, the resists used in shrink processes have been i-line or KrF resists, and if the same shrink processes are used with resists that include a resin containing structural units derived from methacrylate ester units as the primary units, such as the resins used within ArF resists, then the merits of the shrink process in enabling miniaturization of the resist pattern are difficult to achieve.
Accordingly, an object of the present invention is to provide a resist composition that enables formation of a favorable resist pattern using a shrink process in which following formation of the resist pattern, a treatment such as heating is used to narrow the resist pattern, and also to provide a laminate and a method for forming a resist pattern that use such a resist composition.